Decomposition and permeability of room temperature vulcanizing (RTV) silicone

Abstract

Room temperature vulcanizing (RTV) silicone rubber is used to join thermal protection system (TPS) tiles and attach the entire TPS system to the surface of the capsule. The RTV allows expansion and contraction from temperature changes during atmospheric entry, which avoids cracks in the brittle TPS tiles. Two types of RTV are heated to various temperatures at different heating rates in an oven and a thermogravimetric analyzer to understand the decomposition of RTV during the entry process. X-ray computed tomography is used to create three-dimensional virtual volumes of the RTV material decomposed in an oven. The X-ray computed tomography (XRCT) volumes and the mass loss curves from the thermogravimetric analyzer are used to understand the structure of RTV as it decomposes. It is found that RTV material burns from the inside, creating cavities inside the material while pushing the exterior material outwards. This causes inelastic deformation of the RTV material. The two RTV samples decompose in different patterns depending on the heating rate, but the internal decomposition process is consistent with both materials forming cavities, eventually resulting in a permeable material that allows gases to flow through them. It is found that the RTV is impermeable from temperatures between 200 to about 350 ◦C, where the mass decomposition is not significant to be accounted for. However, after 350 ◦C, the mass decomposition significantly increases, making the RTV permeable. The three-dimensional volume of RTV obtained after heating to 600 ◦C is used as an input to compute the effective permeability of the decomposed RTV material.